1. Field of the Invention
The present invention relates to a focal plane shutter having a leading blade group and a trailing blade group composed of a plurality of blades particularly consisting of light shading thin plates.
2. Description of the Prior Art
Generally this type of focal plane shutter is so designed that the leading blade group and the trailing blade group run upwardly and downwardly so as to open and close the exposure opening, with both blade groups being loaded and with both, being folded, above and beneath the opening when the opening is not covered. In consequence, in case the number of blades is small the size of the blades must be large with the result that the blade loading spaces above and beneath the opening have to be large, which increases the size, especially the height of the camera.
In order to overcome the above shortcomings it is desirable for the number of the blades to be increased so as to make the size of the blades small.
In the state where the shutter blades cover the opening, the edges of the blades of this kind of shutter overlap each other, and the width of the overlapped parts is sought to be about 4 mm in order to prevent light leakage.
Consequently, taking the above into consideration, it is desired that the number of the blades should be about 5-7 for a camera in which 35 mm film is used.
In this case it is desired that the blades be held in parallel by means of two arms in such a manner that along with the rotation of the arms around fixed shafts the blades are translated in parallel to the upper and the lower edge of the opening. Thus, when the number of the blades is large the number of the shafts on the arm becomes large so that the length of the arms must be large in order to avoid interference of the blades with the shafts. This makes the horizontal size of the shutter large.
A shutter is known which is so designed that only one of the blades for forming the slit is translated in parallel while others are rotated around one shaft along with the rotation of the above arms. However, in this case the forms of the cam grooves to be provided in the blades become complicated so that smooth shutter operation cannot be expected or the opening covering efficiency is inferior, which is inconvenient.